Method of preseasoning green or partially seasoned wood



United States Patent METHOD-F PRESEASONING GREEN 0R PARTIALLY SEASONEDWOOD Ralph H. Bescher, Pittsburgh, Pa., assignor to Koppers Company,Inc., a corporation of Delaware No Drawing. Filed Feb. 16, 1962, Ser.No. 173,774

6Claims. (Cl. 34-95) This application is a continuation-in-part of mycopending application Serial No. 821,661, filed June 22, 1959, and nowabandoned. v

This invention relates generally to the preservation of wood in a mannerto preseason the Wood in a fire-proof hazardless process by means ofliquefied petroleum gas.

A common practice in the wood preserving industry is to season Woodprior to, during or after impregnating the wood with a preservative. Aconventional method of seasoning wood has been to air dry the wood, thatis, the wood is placed or stored in a lumber yard to await the naturalevaporation and evacuation of the water from the wood.

It is well known that green lumber containswater in two differentconditions, that is, a portion of the water is free in the wood, whereasthe remainder is actually bound in the cellulosic material of the woodand is considered to have saturated the fibers of the Wood. This airdrying method of seasoning is primarily used to remove the free Watercontained in green Wood. The green or unseasoned Wood that is exposed tothe open air but protected from rain will gradually dry out until thegreatest portion of the free water has been removed. The normalprocedure in the .WOOCl preserving industry,

after air seasoning is completed, is to place this pre seasoned Woodinto a kiln and'under high temperatures force as much of the remainingwater as possible to evaporate from the wood. 1

The commonly used method of air seasoning wood has not proven entirelysatisfactory because of the excessive costs necessitated by'the lengthof time required to remove the water in this manner, and because of thehigh inventory of wood which must be kept on hand during the time theseasoning is taking place in the air. Additionally, sapwood material andthe heartwood of nondurable species may become infected with decay(storage rot) in the seasoningv pile especially during warm, humidweather.

In addition to seasoning lumber, it has been common practice to treatwood chemically, either before the lumber has been dried or after'dryinghas occurredto increase the service life when the wood is'to be usedunder conditions that favor the early deterioration of the wood as bydecay, insects and other destructive agencies. This treatment of Wood isgenerally carried out by forcing preservative chemicals into the wood bypressure. Conventionally, this treatment involves subjecting the wood toa predetermined air pressure (super atmosphericor subatrnospheric) andwithout releasing this pressure, introducing a bath of a preservativeonto the wood, then increasing the pressure and usually elevating thetemperature of the preservative nearly to the boiling point of water andmaintaining this elevated pressure for an interval of time to obtain thedesired injection of the preservativein the wood. Thereafter, the bathof preserva tive is removed from the wood and the wood is sub- 73,199,211 Patented Aug. 1o, lass jected to sub-atmospheric pressurewhereby excess preservative solution is removed from the Wood.

The pressure treatment of wood is conventionally dewood. These twoprocesses difier mainly in the initial treating steps. The wood issubjected to sub-atmospheric pressure in the full-cell process so as toempty the cells of air-before the wood is subjected to the bath ofpreservative, and the wood is placed under super-atmosphe'ric airpressure in the empty-cell process to force a considerable amount of airinto the cells of the Wood before subjecting the wood to a bath ofpreservative so that When the pressure is released, the air in the cellswill eject some of the preservative from the cells.

Conventionally, an aqueous or an oil solution of a preservative is usedas the bath. The aqueous or oil solvent places the preservative in aform that will penetrate the cells of the wood; If the wood to beimpregnated is green, that is, it has not been air seasoned, a greatamount of water will be present. If the cells of the wood contain thisgreat amount of water, it follows that in attempting to impregnate apreservative solution into the wood, the water already contained thereinwill resist to some extent the penetration of the preservative. As aresult, the efiiciency of the impregnation process is reduced.Additionally, the presence of the water is undesirable after thepreservative is in the wood. The use'of Water as a carrier for thepreservative will increase the amount of water left in the wood and thusrequires that the wood be dried subsequent to the impregnation with thepreservative. The subsequent drying, of course, requires extra heat andtime and is somewhat dif ficult as the wood cell normally includeswater. The moisture content of thoroughly seasoned wood is, forexample,within the'range of 6 to 15 percent of the dryv weight of. the wood.Also, the wetting during impregnation and the subsequent drying tends tocause checking of the wood and an undesirable raising of the grain.

The air drying methodfor seasoning wood hereinabove discussed hasincluded a slow evaporation of the water while the wood is standing inthe air for long periods of time. This drying period may extend for from3 months to three years depending on the particular species of woodbeing dried. The principal object of this invention is to obtain animproved process for preseasoning green or partially seasoned lumber toobtain a product which (a) does not require an air seasoning period, (b)need not be kept in inventory for any length of time prior to kilndrying or impregnation with a preservative, (c) has had the free waterremoved within a 24 hour period, (d).is not subected to excessive heat,(e) is not damaged by treat ment, and (f) has not been changed in size.

It hasnow been found, in accordance with this invention, that wood maybe readily preseasoned (free Water removed) by subjecting the Wood totreatment with an aliphatic hydrocarbon which (a) boils below theboiling point of water at ambient atmospheric pressure, but (b) readilyliquefies' at ambient atmospheric temperature when placed under elevatedpressure. p

In the process of this invention, the wood is subjected to apredetermined pressure and then without change in pressure is subjectedto .an aliphatic hydrocarbon so that the pressure is increased to injectthe hydrocarbon into the wood and thereafter the hydrocarbon evaporatesfrom the wood.

Using the process hereinabove described, it is possible to remove thefree water contained in green or in partially seasoned wood by themechanical action of the hydrocarbon when it leaves the wood.

The novel process of this invention is applicable to all commercialspecies of wood. In fact, it has been found that the process of thisinvention is applicable to preseasoning refractory species (thosespecies of wood which resist penetration more than the conventionalspecies).

The above defined method of preseasoning lumber is economically andconveniently effective in apparatus commonly used for pressure treatmentof lumber. In this respect, it is a novel method of removing the freewater from green lumber in that while other processes of impregnationwill normally leave water in the green lumber during pressureimpregnation or will attempt to evaporate the water with excessivetemperatures, the novel process of this invention is a mechanicalprocess wherein the water is literally kicked out of the wood by theexpanding aliphatic hydrocarbon gas. As a result of the novel mechanicalremoval of water, there is no checking of the wood nor undesirable timeconsuming, waiting period prior to kiln drying or impregnating the woodwith a preservative.

The novel process of this invention will remove at least 50% of the freewater contained in green or partially seasoned wood. The amount of waterremoved during the processing will, of course, depend upon the speciesof wood being treated. For any species, however, at least 50% of thefree water is removed. The removal of this amount of water from wood inthe very short period of time (less than 24 hours) is a totallyunexpected, unusual and novel result. Since it has heretofore beencommon to air season for up to three years certain species of lumber,the removal of at least 50% of the free water from wood according to theprocess of this invention makes this invention an extremely practicaland time saving method for preseasoning green or partially seasonedwood.

Suitable hydrocarbons for use in accordance with this invention include,for example: liquefied petroleum gas, butane, isobutane, propane, etc.The boiling point and heat of vaporization of these hydrocarbons is suchthat the temperature and heat of the wood itself is sufhcient so that,when the wood is removed from contact with the bath and the pressurelowered, this heat stored in the wood will vaporize the solventremaining on and in the wood.

Accordingly, the process is desirably carried out at temperatures andpressures at which the solvent will be self-evaporating from the woodwhen the bath is removed from the wood. These hydrocarbons have vaporpressures such that the wood can be heated from 150 to 200 F. withoutdeveloping excessive pressure. The application of high pressure to thewood has a tendency to damage the wood by crushing the cells of thewood. In addition, temperatures higher than 200 F. tend to weaken thecell structure of the wood so that the wood becomes more susceptible tocrushing under pressure.

The processing of wood in accordance with this invention, wherein woodis preseasoned in a low boiling hydrocarbon has manifold advantages. Thetreated wood is clean; there is a decrease in weight of the wood; sincethe hydrocarbon has no aflinity for wood, as does water, and since thevapor pressure of the hydrocarbon is greater than the final pressure inthe treating chamber, the hydrocarbon readily escapes from the wood.Thus, air storage is not required. The hydrocarbon itself serves as :aninstrument for removing the residual free water from the wood, i.e., atthe conclusion of the pressure phase, the rapidly expanding solventgases expel the free water from the wood. The wood treated in accordancewith this invention leaves the bath substantially dimensionallyunchanged. Wood treated in accordance with this invention is odorlessand has a non-oily surface, an advantage, of course, if the wood is tobe painted.

The empty cell process is advantageously used to afford a fireproof,hazardless procedure with this process, as the high vapor pressure ofthe solvent aids in the ejection of the hydrocarbon from the cells atthe end of the pressure treating step of the process, thereby reducingthe quantity of hydrocarbon which must be evaporated from the wood. Thegas used for impregnating the cells prior to their impregnation with thesolvent and preservative may be air, but preferably is nitrogen, carbondioxide, or other inert non-condensable gases since the hydrocarbons areflammable. The empty cell process may be used with complete safety andfreedom from fire or other hazardous conditions even though the vaporpressure characteristics of the solvent lends itself to full cellprocess.

The invention will be illustrated further by comparison of the emptycell process in Example II with the full cell processes in Examples 1and III in the following examples.

EXAMPLE I Green timbers of southern pine are placed in a closed cylinderand a vacuum of 25 inches of mercury is maintained on the cylinder forone half hour. Then, without admitting air, the cylinder is filled withliquid butane. The cylinder is then heated until the pressure in thecylinder increases to l25200 pounds per square inch guage. During theheating period, additional solution is pumped into the wood and tomaintain the pressure at -200 pounds per square inch gauge pressure, andthese pressures and temperatures are maintained on the wood for abouttwo hours. Then, the hydrocarbon solution is removed from the cylinderand the cylinder subjected to a vacuum of 25 inches of mercury for anhour. Thereafter, the wood is removed from the cylinder. The wood issubstantially dry, clean and odorless.

EXAMPLE II Green timbers of southern pine are placed in a closedcontainer and air in amounts beyond :the explosive limits, or nitrogenor carbon dioxide, is injected into the container until the pressure inthe container reaches 50 pounds per square inch gauge. Thereafter,butane is forced into the container and air is withdrawn from thecontainer at a rate to maintain a constant pressure of 50 pounds persquare inch gauge in the container. After the solution fills thecontainer, the pressure is increased to 200 pounds per square inch gaugeby raising the temperature, this pressure maintained for two hours, andthen released. As soon as this pressure is released, the compressed gasin the wood expands and forces the hydrocarbon from the wood to aconsiderable extent. The hydrocarbon is drained from the cylinder andthe wood subpected to a vaccum of 25 inches of mercury for a period ofan hour, during which time the heat in the wood evaporates the solventremaining.

EXAMPLE III Green southern pine is placed in a closed container andsubjected to steam at a pressure of 15 pounds per square inch gauge forsix hours. The steam is released and the cylinder evacuated for a periodof two hours. Thereafter, butane is pumped into the cylinder, and afterthe butane fills the cylinder, the butane is heated to increase thepressure to about 200 pounds per square inch gauge and this pressuremaintained for two hours. The pressure is then released and the woodsubjected to a vacuum of 25 inches of mercury for a period of thirtyminutes. The wood presents a product that has been partially dried inless than 10 hours.

EXAMPLE IV Hard maple 1" by 3" by 4 is placed in a closed con trainerand subjected to steam at a pressure of 15 pounds. per square inch gaugefor 6 hours. The steam is released and the container evacuated for aperiod of 2 hours. Thereafter, isobutane is pumped into the containerand,

after the isobutane fills the container, the isobutanc is heated toincrease the pressure to about 200 pounds per square inch gauge and thispressure maintained for 2 hours. The pressure is then released. and thenfollowing this release of pressure, another pressure period ofapproximately 2 hours is again applied to the maple in the I cylinder.Then pressure of the second pressure period is released and the wood issubjected to a vacuum of 25 inches of mercury for a period of 30minutes. The wood is then removed from the cylinder and the moisturecontent is measured. For'these particular species of wood the molsturecontent was reduced from 57% to 36%.

EXAM PLE V Stump green southern yellow pine poles were seasontreatedwith isobutane. A total of 7 hours pressure was used followed by a 2hour final vacuum. The poles had average butt diameters of in. and were36 ft. long. During treatment, the weight per cubic foot of these poleswas reduced from 59.6 to 44.0 lbs./cu. ft.

EXAMPLE VII Stump green southern yellow pine poles were treated andseasoned with isobutane. A total of 7 hours pressure was used followedby a 2 hour final vacuum. These poles had an average butt diameter ofi0" and were 36' long. The average moisture content of the outer l in.of these poles was 65% beforetreatment and 33% after treatment.Approximately 11.7 lbs. of water was removed per cubic foot of wood. 1As further verification of the ability of this. process'to remove thefree water contained in green or partially seasoned lumber, severalother' specimens of southern yellow pine and redwood lumber weresubjected to treatment with liquefied petroleum gases and tested formoisture content before and after treatment. The results of thetreatment of the southern yellow pinespoles are shown below. in Table I.

Table I SEASONXNO DATA ON sou'rnsaN YaLnow rma POLES Moisture Content(Percent) Dimensions Polo Outer t" r" to m" Wt.

Dim, Length, Cubic Before After Bolero After ei.

in. Ft. Feet irest- Treat- Treat- Treatmeat snout assent meat 1 10.: as?one rss 42 a: at 2 m2 sas at: 92 or we 0.1 80.0 is. M 89 M 47 n.4- Milone we so or as ms am no no or us so 0 IOJ 36.6 NJ ill 60 H0 48 use cancar 124 as or an ass 11.0 or as ms to ma ass no or as n so months andthen kiln dry it toa final moisture content of about l0%. Usingtheprocess ofthis invention, the

moisture level of heavy or medium segregation can be immediately reducedto about in less than 24 hours, obviating the use orthe need of anyprolonged air seasoning. Table it shows the resultsof'2l specirnens ofredwood lumber which were preseasoncd' according to 1 this invention andthen measured for moisture content after seasoning.

Table II BEASONXNG DATA ON REDWOOD LUMBER [Dimensions 2 x 6 X 81Moisture Content (Percent) Moisture Board No. Wt. Loss, Content tin/c1.Reduction Before After (Percent) Treatment Treatment 46 29.0 105'. 4629.4 106 lit 00 --l0.0 M 1H 63 l3.2 61 181 61 l9.0 70 I llil 61 -18. 570 m as -a1.o tea m 10 -26. 0a 17'] 64 --26. 7 ms for the removal ofhydrocarbon. The solvent, in addition to self-evaporation from thewood,'creat'cs a me.-

chanical force which removes the free water contained in v green orpartially seasoned lumber and thus exerts apreseasoning effect upon theWood.

What is claimed is: 1. A method of rapidly preseasoning green andpartially seasoned wood which comprisesthe steps of f subjecting saidwood to a predetermined pressure with' inert noneondensable gas so as toimpregnate the wood with said gas, and thereafter without changing thepressure,

subjecting said wood to an aliphatic hydrocarbon which boils below theboiling point of water but which can be liquefied at ambient temperatureconditions at pressurev above atmospheric pressure and which is aliquefied petroleumgas selected from the group consisting of butane,isobutane, propane and isopropane,

subjecting said 'wood and hydrocarbon to increased pressure whereby thehydrocarbonpenetrates said wood as a liquid, and

thereafter releasing the pressure, thereby expanding the non-condensablegas and evaporating the hydrocar bon and thus expelling the free waterand removing the hydrocarbon from the wood.

2. A method of quickly prcseasoning green and partially seasoned woodbyremoving the free water therefrom. which comprises the steps of: V

subjecting said woodto a predetermined pressure with inertnon-condensable gas so asto impregnate the wood with said gas,thereafter, without changing thepressure, subjecting said wood to analiphatic hydrocarbon which boilsbelow the boiling point of water butwhich can be liquefied at ambient temperature conditions at pressuresabove atmospheric pressure and which is a. liquefied petroleum gasselected from the group consisting of butane, isobutane, propane andisopropane, subjecting said 'wood and hydrocarbon to increased: pressurewhereby the hydrocarbon penetrates said" wood as a: liquid,andthereafter-evaporating the hydrocarbon from the wood 7 from the'wood,and whereby said preseasoning occurs in less thana 24-hour period.

3. A- process for preseasoning green or partially sea soned lumber toobtain a product'which does not require an air seasoning period, neednotbe kept in'inventory for a length of time prior to kiln drying orimpregnation with a preservative, and lias'at least 50% of 'the freewater removed within a 24-hour period, the

process: a.

subjecting said wood to an elevated pressure with an inertnon-condensable gas so as to impregnate the wood with said gas,

thereafter without changing the pressure, subjecting said wood to alower aliphatic hydrocarbon which boils below the boiling point of waterbut which can be liquefiedat ambient temperature conditions atpreswhereby the free water is expelled and hydrocarbon is removed fromthe wood to provide a preseasoned wood which is dry in that at least 50%of the free water has been removed therefrom and which has a non-oilysurface. 4. A process of rapidly presessonlng green and partiallyseasoned wood which comprises:

impregnating wood with a liquid hydrocarbon which is a liquefiedpetroleum gas selected from the group consisting of butane, isobutane,propane and isopropane under superatmospheric pressure, and releasingsaid pressure so that said hydrocarbon autogenously vaporizes and thevapors expel the free water in liquid form from the wood. 5. A processof rapidly preseasoning green and partially seasoned wood whichcomprises:

injecting a liquid hydrocarbon which is a liquefied of'butane',isobutane, propane and isopropane into wood,-

heating said wood andhydrocarboniunder pressure,

i and 4 releasing said pressure to from the wood. 6. A method ofpreseasoning green and partially seasoned wood which comprises the stepsof subjecting said wood to a liquid aliphatic hydrocarbon which is aliquefied petroleum gas selected from the group consisting of butane,isobuta'ne, propane and isopropane,

subiectingsaid wood and hydrocarbon to increased pressure'whereby thehydrocarbon is injected into said wood as a liquid, and

thereafter releasing the pressure and evaporatingthe hydrocarbon andthus expelling the free water as a hydrocarbon from the wood.

Q RefereheesCitedbytheEsamlner UNITED STATES PATENTS 1,023,745 4/12 Marr117-59 1,760,444 5/30 Secord 349.5 X 1,967,990 7/34 Edwards 34-95 X2,152,665 4/39 Rosenthal 34-37 X 2,507,190 5/50 Barksdale 349.52,860,070 11/58 McDonald.

6/59 Hutchinson 34-9.5

OTHER REFERENCES Encyclopedia of Chemical Technology, vol. 7, pages 632and 639, 1951 Ed., The Interscience Encyclopedia lnc., NY. 7

Encyclopedia of Chemical Technology, Vol. '10, 1953, page 138, Thelnterscienoe Encyclopedia Inc., New York.

NORMAN YUDKOFF, Primary Examiner.

petroleum gas selected from the group.consisting" vaporize, saidhydrocarbon so that the vapors expel the freewater as a liquid UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,199,211August 10, 19c

Ralph H. Bescher It is hereby certified that error appears in the abovenumbered petent requiring correction and that the said Letters Patentshould read as corrected below.

Column 4, line 27, after "the", first occurrence, insert cylinder toreplace the material forced into the lines 50 and 51 for "subpected to avaccum" read subjected to a vacuum column 6, line 47, for "pressure",

first occurrence, read pressures Signed and sealed this 29th day ofMarch 1966.

(SEAL) Attest:

ERNEST W. SWIDER \ltesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A METHOD OF RAPIDLY PRESEASONING GREEN AND PARTIALLY SEASONED WOODWHICH COMPRISES THE STPES OF: SUBJECTING SAID WOOD TO A PREDETERMINEDPRESSURE WITH INERT NON-CONDESABLE GAS SO AS TO IMPREGNATE THE WOOD WITHSAID GAS, AND THEREAFTER WITHOUT CHANGING THE PRESSURE, SUBJECTING SAIDWOOD TO AN ALIPHATIC HYDROCARBON WHICH BOILS BELOW THE BOILING POINT OFWATER BUT WHICH CAN BE LIQUEFIED AT AMBIENT TEMPERATURE CONDITIONS ATPRESSURE ABOVE ATMOSPHERIC PRESSURE AND WHICH IS A LIQUEFIED PETROLEUMGAS SELECTED FROM THE GROUP CONSISTING OF BUTANE, ISOBUTANE, PROPANE ANDISOPROPANE, SUBJECTING SAID WOOD AND HYDROCARBON TO INCREASED PRESSUREWHEREBY THE HYDROCARBON PENETRATES SAID WOOD AS A LIQUID, AND